It is well known that an ever-increasing number of organizations are using radio communication systems for coordinating their activities. Such organizations include -- among others -- fire departments, ambulance-dispatching systems, and police systems. These radio communication systems are continually exposed to the disturbing effects of other systems, as well as to the disturbing effects of devices such as radio-controlled garage-door-openers, electric razors, diathermy machines, home appliances, and the like; these systems and devices contributing a bedlam of "static" that tends to interfere with the radio communication systems. Since many of the organizations that use these radio communication systems are emergency-type organizations wherein it is essential that communications between the various stations thereof be maintained at all times, it is increasingly important to provide ever-improved communication systems.
For purposes of explanation only, the present invention will be discussed in terms of its use by police department, whose communication requirements ar extremely complex because it has personnel in helicopters, in automobiles, and on foot; it being essential that these individuals keep in touch with each other, and with certain other portions of the organization. Furthermore, the communication system is in constant use, with an ever-changing number of simultaneous communications between ever-changing stations. Moreover, there is the constant danger of one of the stations falling into the hands of a criminal. In addition, it is frequently necessary that a conference-type call be initiated to correlate the activities of a small group of individuals, without disturbing the other capabilities of the system; and that an override-command call be initiated, so that one individual can override all other communications, and cause each person in the system to hear his commands.